Source plaque for an irradiation chamber of curvilinear cross section

ABSTRACT

An elongated tubular source plaque for an irradiation chamber of curvilinear transverse cross section is formed by elongated radiation source members curved to the same curve as the curvilinear section of the irradiation chamber, and the members are spaced apart along the axis of the chamber. Each member is a tube filled with a number of individual sources may be connected end to end to form an annulus, or formed as a helix to provide the tubular source plaque. The members may be of uniform or nonuniform dosage and the spacing of the members may be regular or irregular, and may further be adjustable.

United States Patent inventors Appl. No. Filed Patented Assignee SOURCE PLAQUE FOR AN IRRADIATION CHAMBER OF CURVILINEAR CROSS SECTION 2 Claims, 6 Drawing Figs.

US. Cl 250/106, 250/84 lnt. Cl G2lh 5/00 Field of Search 250/ 106, 106 (S), 84

[56] References Cited UNITED STATES PATENTS 3,153,725 10/1964 Attix 250/106(S) Primary Examiner-Ralph G. Nilson Assistant ExaminerA. B. Croft A ttorney Sughrue. Rothwell, Mion. Zinn & Macpeak ABSTRACT: An elongated tubular source plaque for an irradiation chamber of curvilinear transverse cross section is formed by elongated radiation source members curved to the same curve as the curvilinear section of the irradiation chamber, and the members are spaced apart along the axis of the chamber. Each member is a tube filled with a number of individual sources may be connected end to end to form an annulus, or formed as a helix to provide the tubular source plaque. The members may be of uniform or nonuniform dosage and the spacing of the members may be regular or irregular, and may further be adjustable.

SOURCE PLAQUE FOR AN IRRADIATION CHAMBER OF CURVILIN EAR CROSS SECTION The invention relates to a source plaque for gamma irradiators of curvilinear cross section and with this source plaque it is possible to adjust distribution of dosage within the contained and surrounding volume.

In the irradiation of materials with gamma energy, it is known to place the material to be exposed in a generally cylindrical volume surrounded by a source of gamma energy. The gamma energy is provided by rods extending axially of the cylindrical volume. In this prior art a relatively uniform distribution of dose along the axis of the cylindrical volume can only be obtained by distributing the gamma-emitting isotope nonuniformily along the axis of the source rods with the ends having a higher concentration of gamma-emitting isotopes than the center. This requires either the use of a source material of difi'erent activities along the lengthof source rods or the discretionary spacing of active material with inert matter, a practice which not only makes the cost of the source fabrication higher than it might otherwise be, but also requires significant effort in calculating and measuring source distribution to assure the desired uniformity of dose.

The present invention provides a unique source plaque for irradiation chambers of curvilinear cross section which allows a predetermined dose distribiition to be achieved using relatively uniform activity sources and to be achieved empirically, subsequent to fabrication of the sources, with little calculation required.

In this invention spaced, curved elongated radiation members are formed by a number of individual sources within tubes which are curved along the same axis as an irradiation chamber of circular cross section. The distances between each spaced member which extends generally around the irradiation chamber along the axis of the chamber allows a desired dose distribution to be obtained. The curved elongated radiation members may be formed either as spaced rings or a helix with spaced turns.

Other features of the invention will be pointed out in the following description and claims and illustrated in the accompanying drawings, which disclose by way of example, the principle of the invention and the best mode which has been contemplated of applying that principle.

In the drawings:

FIG. I is a perspective view of a prior art tubular source plaque;

FIG. la is a graph of the dose distribution obtained from the source plaque of FIG. 1;

FIG. 2 is a perspective view of one form of source plaque of this invention;

FIG. 3 is a perspective modification of the source plaque of this invention for achieving the nonuniform dose distribution;

FIG. 3a is a graph of nonuniform dose distribution;

FIG. 4 is a perspective view of a further modification of this invention showing the spacing of the individual radiation source rods of more or less uniform activity to achieve the uniform dose distribution.

In FIG. I which is prior art, gamma-emitting material is fabricated into rods which are placed in an annular space 11 surrounding an irradiation chamber 12 and may be held by end rings 14. If the distribution of gamma-emitting material along the axis of rods 10 is uniform, the dose distribution within the cylindrical volume approximates a truncated cosine distribution as shown in FIG. la.

FIG. 2 shows a stack of curved radiation source members of this invention which have been formed into rings or individual toroids and are evenly spaced. The dose distribution in the contained volume of the cylinder would be the same as in FIG. la if the individual sources were all of the same activity. The individual source rings in FIG. 2 are located along a common axis and are held by spacers or holders to vary the distance between each ring until a desired dose distribution is obtained. A fixture illustrated schematically at 18 having holders 20 may hold each of the individual rings 16. The rings are formed from curved tubes 22 each containinga plurality of individual sources 24. It IS not necessary that t e individual sources 24 themselves be uniform in activity along their length but subsequent applications are simplified if they are.

The spacers or holders 20 of the support 18 may be varied to vary the distance between each ring until a desired close distribution is obtained. The fixture may be permanent or temporary; however, if a temporary fixture is used for establishing dose distribution, the ring should be assembled into a permanent fixture so as to repeat the configuration of the assembly on which the dosimetry had. been performed. Alternatively, the source fixture may be equipped with means to ad- 20 just the spacing between rings so as to permit subsequent redistribution of the dose within the irradiation chamber.

As shown in FIG. 3, the invention may be implemented by providing a number of straight sources within a tube and bending the tube to form a helical coil. The spacing between helices can be adjusted to obtain a desired dose distribution whether that distribution be uniform or nonuniform. FIG. 3 as shown achieves a nonuniform distribution of FIG. 30 by using sources of unifonn activity and in the bottom portion of the source chamber the rings of helix are closer together.

FIG. 4 shows a further modification of this invention wherein an arrangement of the dosage rings are spaced apart at the center to achieve uniform dose distribution using sources of uniform activity.

Uniform dose distribution may also be achieved using a relatively uniform spacing as in FIG. 2 provided that higher than average activity sources are used at the ends of the irradiation chamber, and lower than average activity sources are used in the center.

Also, as the source decays, with the construction of FIG. 2 one may maintain source strength as well as uniform dose dis tribution by adding new sources at the ends, moving older sources toward the center, and removing the oldest, lowest activity sources from the center of the plaque.

The practice of this invention is not limited to circular geometry as the tabular source plaque may be circular, elliptical, or any other curvilinear transverse cross section. The source plaque may be on either vertical, horizontal, or any other axis as this invention permits a great diversity in arrange ments of chamber and orientation. Other variations may be made within the teachings of this disclosure without departing from the spirit and scope of this invention as defined by the appended claims.

It is claimed:

1. A tubular source plaque for an irradiation chamber of curvilinear cross section, the source plaque comprising: a plurality of radiation source members formed as annular rings of substantially the same cross section as the curvilinear cross section of the irradiation chamber and extending generally around a long axis of the chamber, each of the members being formed from elongated tubes uniformly filled with individual radiation sources of predetermined strength, and means for spacing these members along the longitudinal axis of the irradiation chamber in a predetermined manner to obtain a uniform dosage throughout the length of the chamber.

2. A radiation source as defined in claim 1 wherein the spacing means spacing the members is capable of adjustment. 

1. A tubular source plaque for an irradiation chamber of curvilinear cross section, the source plaque comprising: a plurality of radiation source members formed as annular rings of substantially the same cross section as the curvilinear cross section of the irradiation chamber and extending generally aRound a long axis of the chamber, each of the members being formed from elongated tubes uniformly filled with individual radiation sources of predetermined strength, and means for spacing these members along the longitudinal axis of the irradiation chamber in a predetermined manner to obtain a uniform dosage throughout the length of the chamber.
 2. A radiation source as defined in claim 1 wherein the spacing means spacing the members is capable of adjustment. 